Dry process for making composite products with ph control



E. G. HALLONQUIST DRY PROCESS FOR MAKING COMPOSITE PRODUCTS WITH PHCONTROL Filed NOV. 21, 1948 Oct. 16, 1951 .2; 3:5 6 m Q h 0 h if 833% uw M 3m 6Q 9Q wgwwwkm ut wqbmwkow e Z) -ouaaos9v. 831m INVENTOR Earl Glly/0W0,

A TTDRA/EYS Patented Oct. 16, 1951 DRY PROCESS FOR MAKING COMPOSITEPRODUCTS WITH pH CONTROL Earl G. Hallonquist, Tacoma, Wash., asslgnor toPlywood Research Foundation, Tacoma, Wash., a corporation of WashingtonApplication November 21, 1949, Serial No. 128,665 8 Claims. (01. 18-475)This invention relates to a process for making composition boards andrelated products by the consolidation of dry or moist sheets or feltscomposed of pieces of lignocellulose materials, e. g. wood fibers.

The present invention is based upon the discovery that, in themanufacture of consolidated products by the dry process, the pH of thelignocellulose mixture immediately prior to its consolidation, is ofcontrolling importance in determining the water resistance properties ofthe consolidated products. According to the present invention it hasbeen found that, where such pH of the mixture exceeds a value of about6.0, the water IBSlSt'Zl'lOG characteristics of the product areaifectec'. adversely, this efiect increasing rapidly with increase in pHvalues. However, if the pH of the mixture is kept below a value of about6.0, the water resistance properties of the product are markedlyimproved.

Hence, broadly stated, the process of the presem; invention comprisesproducing a consolidated product having desirable properties of waterresistance by forming a dry mixture of pieces or particles of wood orrelated lignocellulose materials with suitable quantities of binder andother additives, adjusting the pH of the mixture to a value of less thanabout 6.0, and consolidating the resulting mixture of controlled pH bythe ap plication of heat and pressure. When this is done, theconsolidated products formed uniformly have low water absorption andswelling properties upon exposure to moisture, regardless of theidentity of the lignocellulose starting material, the nature and amountof the binder and size incorporated in the mixture, and the initialacidity or alkalinity of the lignocellulose starting material and of theadded substances.

Processes for the production of consolidated composition boards,particularly hard board, may be of two general classes. In the wet;process, a low consistency slurry of wood fiber in water containingroughly from 3,000 to 10,000% by weight water (on the basis of the dryfiber) is passed through a screen to form a felt from the suspendedfibers. This felt then is consolidated to the desired degree by theapplication of heat and pressure.

In a dry process, on the other hand, the solid fibers are formed into afelt by mechanical means without suspension in a liquid medium. Theflbers are not dry, however, in the literal sense of not containing anymoisture. They may contain substantial amounts of moisture, such as, forexample, in the order of to 1 such moisture content obtaining because ofthe moisture content of the wood and of the added materials. It is witha dry process that the present invention is concerned. the words "dryprocess" and dry forming into a mat being used herein in the acceptedsense described above, 1. e., in the sense that the lignocellulose rawmaterial is handled in the form of solid pieces or particles withoutsuspending it in a liquid vehicle, although the lignocellulose mixture,just prior to pressing, may have a substantial moisture content. Asuitable dry process in which the process of the present invention isapplicable, is described in the copending application of Schubert etal., Serial No. 51,938, filed September 30, 1948.

It is to be understood that the presently described process isapplicable to llgnocellulose materials which are substantially unalteredchemically from their native condition and which have not been subjectedto the drastic preliminary chemical treatments which are often employed,for example, in preparing lignocellulose material for use in moldingprocedures. In such preliminary treatments the llgnocellulose materialis often extensively degraded, as by hydrolysis.

In the present process, on the other hand, the

lignocellulose material is not subjected to chemical treatment beyond anoptional preliminary steaming calculated only to soften the fibers,thereby facilitating their subsequent mechanical separation as describedherein. There is no extensive hydrolysis of the lignocellulose material,which therefore is employed in the present process in a relativelynon-degraded and nonhydrolyzed condition.

Where the wet process is used, the control of the pH of the felt priorto its consolidation does not present a particular problem since, nomatter what the character and pH of the starting material and additives,and the amounts of the latter which are incorporated in the mixture, theexcess quantities of either acid materials or basic materials are washedaway from the lignocellulose fibers with the very large volumes of waterused as the suspending medium. Therefore the pH of the felt prior to itsconsolidation will not be affected materially by the presence of theadditives, but usually will be a value which is substantially determinedby the pH of the lignocellulose material and water employed. Thesituation is otherwise in a dry process, however, where the washingeffect of large volumes of water is entirely absent. In this case, anyadded alkali or acid remains in admixture with the form of theiraqueous, alkaline solutions in amounts ranging from about 2% up to asmuch as about by weight (solids basis) depending upon the properties itis desired to impart to the product. It will be apparent that the largerthe quantity of such binders used, the greater the quantity of alkali(usually caustic soda) that will be introduced into the lignocellulosemixture. Furthermore, the alkali content of the resinous binder, itself,is widely variable depending upon such factors as its source, its degreeof advancement and the like. For these resasons, unless specialprecautions are taken to adjust the pH of the mixture of lignocelluloseand added binder, the pH of the mixture will be extremely variable fromoperation to operation. When a large percentage of binder is used, orwhen a binder is used having a high content of alkali, the pH of thefelt will be correspondingly high, while if the reverse is true, thefelt pH will be correspondingly low.

Still another complicating factor is the fact that the lignocellulosematerials, themselves, are

characterized by widely differing pH values,

Thus whereas hemlock wood has a pH of about 5.4 and the wood of thewhite fir has a pH of about 5.2, the wood of the Douglas fir isrelatively acid and has a pH of about 3.6. Hence if one of the moreweakly acid woods such as hemlock is used in combination with a largeproportion of a strongly alkaline binder, the result- As has been notedabove, variations in the pH of the lignocellulose mixture are reflectedmarkedly in the water resistance qualities of the consolidated productsmade therefrom. This effect is illustrated in the following examples. Inall of the examples, the raw lignocellulose (wood) in the form of chipsor hog fuel after a preliminary steam treatment was converted to afibrous state in a mechanical grinder or fibrator. The resinous binder,and wax size (if employed) in the form of a water solution or emulsionwere incorporated by adding them to the chips before grinding, or to thefiber after grindi The resulting fibrous mixture then was felted into auniform mat by mechanical means and pressed in a conventional hot pressto remove the moisture and set or cure the resinous binder. A screen wasused on one side of the felt to facilitate moisture removal, and asmooth caul on the other side in order to give a smooth glazed surfaceto the board. The felts were pressed at the temperatures and pressuresand times given in the tables and the resulting consolidated productsremoved from the press.

The water resistance and other properties of 4 cent increase in weightof the soaked sample over its original weight.

The swelling characteristics were determined by soaking a 1" by 6"sample in water under the same conditions as given above, i. e., at F.for 24 hours, and the increase in thickness of the sample measured aftersoaking. The swelling property then was calculated in terms of per centof the original thickness. The pH of the unconsolidated felt (whenmeasuredTwashdetermined by immersing 10 grams of the moist fibercomprising the felt and containhig approximately 60% water based on theoven dry weight of the fiber in ml. of distilled water and then takingthe pH of the resulting slurry after a period of from 16 to 20 hours.The pH of the board resulting from consolidation of the felt (whenmeasured) was determined in a similar manner except that the board waspulverized before immersing in water.

The examples of Table I illustrate the effect of adding varyingquantities of a given binder on the water resistance of the resultingboards.

Introduced as an alkaline aqueous solution of a thermosettinggiggly-formaldehyde resin containing about 40% by weight resin Theexamples of Table II illustrate the effect of the pH of thelignocellulose raw material on the water resistance properties of theconsolidated product.

Table II Example 4 5 0 7 8 9 Felt Composition (per cent by wt. solidsbasis);

White fir fiber (pH-5.54.0) 05 95 95 Douglas fir fiber (pH=3.6-3.9) 9595 95 ax 2.5 2.5 2.5 2.5 2.5 2.5 Binder 2.5 2.5 2.5 2.5 2.5 2.5 PressingConditions:

Pressure (p. s. i.). 150 200 200 1 500/200 500/200 Temperature 190 l00100 190 190 Time (Min l5 l5 l5 15 15 Board Properties:

Water Absorption (percent).. 62. 2 28. 4 57. 2 25. 7 32. 6 l9. 0Thickness Bwelling 28.4 12.8 25.9 12.2 17.1 8.00

I 500 p. s. i. for 36 min; then 200 p. s. i. for 14% min.

The examples of Table III illustrate the effect of adding increasedamounts of alkali to a resin binder used in fixed amounts on the waterabsorption properties of the resulting consolidated products. In thiscase, the products were made up with a fiber mix consisting of 2 /270 byweight (solids basis) phenol-aldehyde resin, 2/2% wax size, and 95%Douglas fir fiber. The resin originally had a sodium hydroxide content(liquid resin basis) of 2%. Additional sodium hydroxide was added asindicated.

the case of highly acid woods such as Douglas it may be necessary to addacid directly to the Table III Example 10 ll 12 13 14 16 16 17 18 19 2021 Felt Composition (per cent by wt.

solids basis):

Douglas Fir Fiber 95 95 95 95 95 95 95 95 95 95 95 95 Wax 2. 5 2. 5 2. 52. 5 2. 5 2. 5 2.5g 2. 5 2. 5 2. 5 2. 5 2. 5 Binder 1 2. 5 2. 5 2. 5 2.5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 N aOH Content of binder (percent) 2 5 7. 5 l0. 2 7. 5 10.0 2 5 7. 5 10. 0 H of Felt 4. 7 5. 5 6. 87. 9 4. 7 5. 5 6. 8 7. 9 4. 7 5. 5 6. 8 7. 9 oisture Content of Felt(per cent) 54. 0 57. 0 62. 0 64. 0 54. 0 57. 0 62. 0 64. 0 54. 0 57. 062. 0 64. 0 Pressing Conditions:

Pressure (p. s. i.) 150 150 150 150 200 200 200 200 500/200 500/200500/200 500/200 Temperature (0.) 190 190 190 190 190 190 190 190 190 190190 190 Time (Min.) 15 15 15 16 15 15 15 Board Properties:

Water Absorption.. 24. 7 29. 6 53.0 19. 0 25.1 44. 6 55. 5 14.1 16.3 33.2 42.1 Thickness Swelling (per cent) 11. 4 13. 9 23. 5 23. 5 8. 9 12. 521. 7 24. 2 6. 4 7. 9 17. 2 22.1

1 Introduced as an alkaline aqueous solution of a thermosettingphenol-formaldehyde resin containing about 40% by weight resin SOlldS.

500 p. s. i. for min.; then 200 p. s. i. for 14% min.

It will be seen clearly from the above examples that consolidatedproducts prepared using increased amounts of binders dissolved inalkaline media, and hence incorporating increased amounts of alkali,have increasingly poor qualities of water resistance. Thus, as shown inTable I, a board made using 2.5% by weight of an alkaline binder has awater absorption of 29.6% while a board made using 7.5% of the samebinder has a water absorption of 42.3%.

Similarly it is apparent that employing a fixed amount of alkalinebinder with lignocellulose materials of varying acidity results in theformation of consolidated products having increasingly good qualities ofwater resistance as the acidity of the lignocelulose material increases.Thus, as is shown in Table II, Examples 8 and 9, composition boards madefrom white fir having a pH of 5.5 to 6.0 have a water absorption of32.6% and a thickness swelling of 17.1% while boardsmade from the moreacid Douglas fir (pH=3.6-3.9) under the same conditions andincorporating the same amount of alkaline binder have a water absorptionof only 19.0 and a thickness swelling of only 8.0%.

Still further, as is shown in Table III and in the drawing wherein thedata of Table III are plotted, increasing the alkaline content of thebinder and hence increasing the pH of the felt containing the same verymaterially increases the water absorption and thickness swellingproperties of the finished boards. It will be apparent, however, thatthis eifect is greatest at pH values above 6.0, changes in pH below thiscritical limit having but comparatively little effect on the waterresistance properties of the boards.

Hence in the manufacture of consolidated boards from lignocellulosematerial by the dry process of the present invention, the pH of thelignocellulose mixture just prior to consolidation is adjusted to alevel below a pH of about 6.0.

The lower pH limit depends upon such factors as the sensitivity of theparticular lignocellulose materials used to acid, and the susceptibilityof the press and handling equipment to the corrosive action of acid.Usually no substantial practical advantages result in employin a pHbelow about 2 while practical results obtain by maintaining a pH in arange of about 2 to 6, a preferred range of pH being about 3 to 5.

The pH of the lignocellulose mixture just prior to pressing, preferablyis regulated by controlling the amount of alkali added to the resinousbinder. This procedure may be employed, for example, in

'lulose mixture.

lignocellulose material or the lignocellulose mixture. Thus when acid isto be added, it may be added at any suitable point durin the procedure,as by adding the same to the lignocellulose material, either before orafter defibering or comminuting, or by adding the same to the resinbinder, or by adding the same to the lignocelchloric acid, sulfuricacid, sulfurous acid, and

phosphoric acid. These may be used preferably in the form of theirdilute aqueous solutions although in certain instances the acidanhydrides, such as sulfur dioxide, may be employed.

.Acid salts such as aluminum sulfate, ammonium chloride or sodium acidsulfite also may be used. Still further and preferably, there may beused the organic acids such as formic acid, acetic acid, propionic acid,and the like. These various acid materials may be used singly or incombination with each other.

After the regulation of the acidity of the lignocellulose mixture, thelatter is formed into a felt by any suitable dry forming means adaptedto produce a uniform layer of the desired thickness. The felt then maybe consolidated by conventional methods and in conventional equipmentunder operating conditions calculated to produce a consolidated productof the desired density. Suitable operating conditions, as set forth inthe examples, comprise pressing at from to 500 p. s. i. at about 190 C.for a time period of about 15 minutes, or in general at from 100-800 p.s. i. and -200 C. for 10-30 minutes.

In the examples illustrated in the drawing, the moisture content of themixture just prior to pressing was in the order of 60% (by weight).Generally speaking, such a moisture content of the lignocellulosemixture requires pressing conditions of about 200 p. s. i. for 15minutes to consolidate a hard board and drive out free moisture withoutdifficulties as to blowing, blistering and spotting. While the curves onsaid drawing indicate that the water absorption qualities improve withincreased pressing pressures, other factors, as the amount of moisturepresent in the mixture, determine the maximum and desired -practlcalpressing conditions. with pressing pressures of over 200 p. s. i. andwith relatively. low moisture content in the mixtures, a pH in the orderof 6.0 will produce satisfactory hard boards. In any event, the saidcurves indicate that the water absorption qualities of boards areimproved by controlling the pH of the mixture to below 6 just prior topressing, regardless of the pressing conditions.

Although the present invention has been described and illustrated interms of wood and the phenol-formaldehyde binders, it will be under-'stood that no limitation is intended thereby and that the invention isapplicable broadly to lignocellulose materials as a class, including thevarious species of wood as well as annual products such as straw, cornstalks, cane and the like in the form of fiber or other pieces orparticles susceptible to dry forming into a mat. Similarly otherresinous binders may be employed in lieu of the phenol-formaldehyderesins. Such binders include, for example, thermosetting resinouscondensation products of cresol and formaldehyde, xylenol andformaldehyde, acetaldehyde and phenol, furfural and phenol, and thelike. Still further comprehended are such other thermosetting resinousmaterials as the urea formaldehyde resins and their analogues.

Having now described the invention in preferred embodiments, what isclaimed is:

1. The process for the manufacture of consolidated lignocelluloseproducts which comprises forming a. mixture of pieces of relativelynon-hydrolized lignocellulose, adjusting the pH of the mixture to avalue of less than about 6, dry forming the mixture into a mat, andconsolidating the mat.

2. The process for the manufacture of consolidated lignocelluloseproducts which comprises forming a mixture of pieces of relativelynon-hydrolized lignocellulose, adjusting the pH 01 the mixture to avalue of between about 2 and about 6, dry forming the mixture into amat, and consolidating the mat.

3. The process for the manufacture of consolidated lignocelluloseproducts which comprises forming a mixture of pieces of relativelynon-hydrolized lignocellulose, adjusting the pH of the mixture to avalue of between about 3 and about 5, dry forming the mixture into amat, and consolidating the mat.

4. The process for the manufacture of consolidated lignocelluloseproducts which comprises forming a mixture of pieces of relativelynon-hydrolized lignocellulose intermixed with a binder therefor,adjusting the pH of the mixture to a value of between about 2 and about6, and consolidating the resulting mixture;

5. The process for the manufacture of con solidated lignocelluloseproducts which comprises iorming a mixture of pieces of relativelynon-hydrolized lignocellulose with a thermosetting binder therefor,adjusting the pH of the mixture to a value oi! between about 2 and about6, dry forming the mixture into a mat, and consolidating the mat by theapplication of heat and pressure.

6. The process for the manufacture of consolidated lignocelluloseproducts which comprises forming a mixture of pieces of relativelynon-hydrolized llgnocellulose with a thermosetting binder comprising aphenol-aldehyde resin, adjusting the pH of the mixture to a value orbetween about 2 and about 6, dry forming the mixture into a mat, andconsolidating the mat by the application of heat and pressure.

7. The process for the manufacture of consolidated lignocelluloseproducts which comprises forming a mixture of pieces of relativelynon-hydrolized lignocellulose with a thermosetting binder comprising anaqueous alkaline solution of a phenol-formaldehyde resin, adjusting thepH of the mixture to a value of between about 2 and about 6, dry formingthe mixture into a mat, and consolidating the mat by the application ofheat and pressure.

8. The process for the manufacture of consolidated lignocelluloseproducts which comprises forming a mixture of pieces of relativelynon-hydrolized lignocellulose and an aqueous alkaline solution of athermosetting phenol-aldehyde resin, adding an acid material to the saidmixture for adjusting the pH of the mixture to a value of between about2 and about 6, dry forming the mixture into a mat, and consolidating themat by the application of consolidating temperatures and pressures.

EARL G. HALLONQUISTI REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PATENTS Goss Sept. 6, 1949

1. THE PROCESS FOR THE MANUFACTURE OF CONSOLIDATED LIGNOCELLULOSEPRODUCTS WHICH COMPRISES FORMING A MIXTURE OF PIECES OF RELATIVELYNON-HYDROLIZED LIGNOCELLULOSE, ADJUSTING THE PH OF THE MIXTURE TO AVALUE OF LESS THAN ABOUT 6 DRY FORMING THE MIXTURE INTO A MAT, ANDCONSOLIDATING THE MAT.